The invention relates to unsaturated homo- and/or copolymerizable polyesters, prepared from an alcohol component comprising a multivalent alcohol, an acid component comprising a multivalent carboxylic acid, and optionally hydroxycarboxylic acids or their derivaties which are capable of forming esters, and wherein the acid component comprises an acid selected from the group consisting of maleic acid, fumaric acid, itaconic acid, mesaconic acid, aconitic acid, their derivatives which are capable of forming esters, and mixtures thereof; a method for manufacturing same and their use.
The manufacture and processing of homo- and/or copolymerizable unsaturated polyesters is known. Unsaturated polyester resins can be produced by copolyesterification of mono- and/or multivalent alcohols with mono- or polyfunctional carboxylic acids and/or, optionally, hydroxycarboxylic acids comprising alcoholic hydroxyl groups or also using or co-using their derivatives which are capable of forming esters. In the process at least one compound which is olefinically unsaturated and homo- or copolymerizable is condensed into the polyester resin, where the average functionality and the ratio of hydroxyl to carboxy groups must be chosen according to rules well-known by the art so that the formation of polyesters is assured. The resultant resins can then be hardened into thermosetting plastics. Thick layers may be formed, preferably by the addition of radical-furnishing compounds, and optionally by the addition of olefinically unsaturated copolymerizable monomer compounds.
These known compounds are used particularly in the form of their solutions in copolymerizable vinyl and/or allyl monomers as casting resins for impregnating electric machines or parts thereof, such as stators of electric motors or transformers. Impregnating methods such as immersion or sprinkling may be employed. Furthermore, electrical or electronic components or complete circuits can be superficially coated.
After the immersion of the machines or components, the latter are conducted through an evaporation and dripping zone and then the adhered polyester resin is hardened in an oven. With this method, dripping losses first occur in the dripping zone. Even though the resin accumulating in this zone can be returned to the immersion tank, there is the disadvantage that the dripping leads to incomplete impregnation. Furthermore, additional dripping losses occur in the oven prior to hardening if the viscosity of the casting resin drops due to the increase in temperature. This is particularly disadvantageous because the material dripping off in the oven is hardened and so cannot be reused. This material also leads to considerable contamination of the oven.
Further problems which result from the dripping-off or running-down of the casting resins is the occurrence of non-uniform layer thicknesses which increase from the top to the bottom of the coated components and the development of beads at the lower edge of coated components.
To avoid these disadvantages it is known to generate structural viscosity or thixotropy in the casting resins by adding to them substances which produce flow anomalies therein. For this purpose, substances such as pyrogenic silica, asbestos fibers, quartz meal, microdolomite or liquid components such as castor oil derivatives, acrylic resins or silicone are used. Several disadvantages are associated with the use of these additives. The inorganic components do not yield clear solutions and it is not always simple to work them into the polyester resins. The above-mentioned liquid components disadvantageously function to soften the resins. Furthermore, skin can develop on the casting resins if these additives are used.
It is an object of the invention to avoid these disadvantages of the state of the art and to create polyesters which exhibit useful flow anomalies due to their molecular structure and exhibit structural viscosity or thixotropic behavior without the addition of supplementary compounds.